This invention relates generally to pressure equalizing devices, and more particularly relates to an apparatus for equalizing pressure exerted by top gas, generated during operation of the blast furnace, on the bottom surface of the large bell movably mounted in the top of the blast furnace.
A blast furnace comprises a tall shaft furnace consisting of a cylindrical bottom hearth portion, from which rises an upwardly-widening conically-tapered bosh portion, surmounted by a taller tapered shaft structure which narrows towards the top, where it is closed by means of a top closing device. Such a furnace is generally used for production of pig iron from charge including metallurgical coke, iron ore, and fluxes, which charge is generally fed thereinto stepwise through the top closing device.
During normal operation of a blast furnace, a substantial quantity of gas which includes carbon monoxide, known as top gas, is generated in the top of the blast furnace. Such top gas exerts full furnace pressure on the bottom surface of a large bell movably mounted in the top of the blast furnace, which pressure is partially counterbalanced by pressure exerted on the opposite (top) surface of the large bell by the weight of the charge thereon and by force exerted thereon by the operating mechanism connected thereto.
Devices used previously to provide additional pressure on the top surface of the large bell to equalize the full furnace pressure exerted on the bottom surface thereof by top gas, to enable opening of the large bell for feeding charge therethrough into the blast furnace, generally included elements located remote from the blast furnace for scrubbing the top gas to remove pollutants therefrom and for directing the scrubbed top gas into the large bell hopper; scrubbing of the top gas to remove pollutants therefrom was necessary since top gas in the large bell hopper was vented to atmosphere when the small bell was opened to feed charge into the large bell hopper.
Blast furnaces are presently being operated at high internal furnace pressures in order to generate more intimate contact of denser mixtures of gas so as to generate greater production and increased efficiency. Such high internal furnace pressures, however, generate high top gas pressure which is exerted on the bottom surface of the large bell such that it interferes with opening of the large bell for feeding charge therethrough into the blast furnace. The remote location of elements in devices previously used to provide equalizing pressure generated substantial pressure drops through such devices, which loss of pressure prevented the use thereof for equalizing such high pressure top gas. Furthermore, such devices previously used included a shutoff valve in the duct leading into the large bell hopper, which valve was subject to improper and incomplete sealing resulting in loss of equalizing pressure, enabling back flow of top gas therefrom upon opening of the large bell for feeding charge therethrough into the blast furnace, and generating the formation of pockets of stagnant gas subject to condensing, freezing or exploding due to ambient conditions thereabout. Still further, such devices previously used included valves in the top gas uptakes leading from the blast furnace which relieved pressure by venting top gas therethrough in the event that a slip developed in the blast furnace generating a sudden pressure surge; such direct venting of top gas to atmosphere, however, also vented the carbon monoxide and dust therein which polluted the atmosphere.